In the early parts of the book, Snowball is a hero of the animals' revolution. He is, in particular, the main hero of the Battle of the Cowshed. But then he loses out to Napoleon in a contest to see who will rule the farm. Napoleon chases him off the farm and starts to blame everything that goes wrong on him. Here are some examples:

He steals the corn

He knocks over pails of milk

He breaks eggs

He tramples on the seed beds where young plants are

He is chewing the bark off of young trees.

Basically every setback is blamed on him so that no one will blame Napoleon for them.